Electrical thermostat



(No Model.)

EH. PRENTISS' t J. A. TILDEN.

ELECTRICAL THERMOSTAT.

No. 285,676. Patented Sept. 25, 1883.

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UNITED STATES P IATTENT EEIcEa FREDERICK H. PEENTISS, OE DOST N, ANDJAMES A. TTLDEN, OE HYDE PARK, ASSIGNOES TO THE AUTOMATIC ETRE ALARMASSOCIATION, OE BOSTON,

MASS A OHUSETTS.

ELECTRICAL THERMOSTAT.

SPECIFICATION forming part of'Letters Patent No. 285,675, datedSeptember 25, 1883.

Application tiled December 7', 1532.

(No model.)

To all 'whom t may oon/eerie:

Be it known that we, FREDERICK Hfnnrr rriss and Janus A. TILDEN,citizens of the United States, residing, respectively, at llos ton, inthe county of Suffolk and State ol" Massachusetts, and at Hyde Park, inthe county of Norfolk and State oi Massachusetts, have invented a newand useful Electrical Thermostat, oi' which the following is aspecitication.

Our invention relates to improvements in electrical thermostats in whichan electric circuit is made or broken by the movement of a movableelectrical conductor, which conduct or is moved at a predeterminedtemperature by the vaporization oi' a volatile liquid contained in asuitable reservoir, which temperature is determined by the propertiesol" the saturated vapor of the volatile liquid used; and the objects ofour invention are to make or break an electric circuit whenever theteniperature of the atmosphere surrounding the thermostat reaches thedegree at which the contained volatile liquid vaporizes. XVe attainthese objects by a device, modifications oi which are illustrated in theaccompanying drawings, in which- Figure l is a vertical section oi' anelectrical thermostat embodying our invention as used on an opencircuit. Fig. 2 is a vertical section of an electrical thermostat, alsoem bodying our invent-ion, as used on a closed circuit. 1

The tube a is shown iilled with mercury between the points j' and g. Theupper end ot' the tube is sealed by fusing in a lampor blowpipe iiaine,and contains a volatile liquid, which completely fills the upper partot' the tube above f. The receiver or holder b consists of a tube ofglass or other suitable substance, the Jlower end of which is fittedwith a rubber cork, d, or other non-conducting material, hollowed out,as shown, and through which pass two wires, E and E. The tube A passesthrough a stopper, c, of cork, papiermache, or other material, whichfits (though not air-tight) the upper part of the receiver b.

The operation of the instrument is as follows: Upon the application ofheat the eXpansion of the mercury and of the volatile liquid, asliquids, causes the mercury to rise above the point g, but not so muchas to cause any ot" the mercury to be i'orccd out ol' the tube o, intothe receiver Z); and we do not claim any movement of ihe mercuryproduced by such expansion. Vhen, however, upon the i'urther applicationof heat, the boiling-point ot the volatile liquid is reached and theforniation oi' vapor ensues, the mercury will be forced out rapidly andinstantly into the receiver b, and thus close the circuit by forming anelectrical connection between the wires or electrodes E and E. Thus, incase sulphuric ether were chosen as the volatile iluid, theboiling-point of which is about 9So Fahrenheit, 6 5 the circuit would beclosed at that temperature. Bisulphide of carbon, the boiling-point ofwhich is about 11SO Fahrenheit, would close the circuit at 118Fahrenheit, and so, also, alcohol at 1720 and water at 212. Othertemperatures may be readily obtained by the use oi' other liquids, amongwhich are the long list of hydrocarbons.

Turning now to our second modihcation, (shown in 2,) -the bent tube ofglass is shown iilled with mercury between the points i' and s on oneside and between the points t and a on the other side, while thevolatile liquid completely iills the tube between the points s and t.The two electric wires 'L' and 'if' are introduced, as shown, andterminate, rcspectively, fi below the ineniscus T and Il below themeniscus u, the mercury between tand Y u thus forming the electricalconnection. The operation is as follows: Vhen, upon the application oihea-t, the boiling-point of the vola tile iluid is reached, the mercuryis depressed in the two legs O and l? and rises in the two legs K and N,and in consequence of the leg N being shorter than the leg K the mercuryovcr- 9o flows from the leg N, exposing the end of the wire i, thusbreaking the circuit.

Other forms can be used, both for open and closed circuits, besidesthese, and we do not confine ourselves to the special forms of theinstrument shown in the drawings.

It will be seen from an inspection of the drawings that, since a verysmall quantity of volatile liquid (much less than here shown) issufficient to drive out the mercury, no deli- Ico cate proportionment ofparts is necessary either oi` the liquids or the glass. It will also beseen that the wires require no accurate adjustment.

Ve are aware that prior to our invention mercury and other liquids havebeen com- 5 bined in electrical thermostats; but heretofore the circuithas been closed or broken by the eX- pansion ofthe liquids as liquidsalone, thereby requiring an apparatus of delicate and expensiveconstruction with ne adjustment of electrodes, thus making theinstrument quite too costly for general introduction, while in ourinstrument the temperature at which the circuit is opened or closed isdetermined solely by the volatile liquid employed, and the temi 5perature at which the signal is given will be at the boiling-point ofthat liquid.- Now, as the vapor is many times the volume ofthe liquid,it is evident from the very considerable movement of the mercury causedthereby that the size of the glass is immaterial, as is also to a greatextent the distance of the electrodes, thus greatly simplifying andlessening the cost of construction. To make the action ofthe thermostatclearer, and to show lprecisely the temperature at which the movement ofthe mercury would be caused by the conversion of the lighter liquid intovapor, -we can take, for example, a thermostat as herein described inwhich the lighter fluid 3c is water. Now, it is evident that the waterwould give oil vapor at a temperature when the tension of the vaporwould just balance external pressure. At the temperature of 212Fahrenheit the tension of the saturated vapor of water is equal to 29.92inches of mercury, and when the atmospheric pressure is also 29.92inches the tension of the water-vapor is just equal to the atmosphericpressure, and the temperature 212O Fahrenheit isr called theboiling-point, the pressure 29.92 being the average height of barometerat sea-level. lf reference be made to Fig. 1, it will be seen, in orderthat a vapor may form from the lighter liquid, the tension ofthe vapormust be equal to the dierence between the atmospheric pressure (asindicated by barometer and expressed in inches of mercury) and thevertical distance g f.` For example, if the height of barometer is 29.92and the mercury column gf is 6.46 5o inches, the actual pressure is2992-646 or 28.46 inches. N ow, the temperature at which the saturatedvapor of water has a tension of 23.46 inches is 200. Fahrenheit, andconsequently the temperature at which such a thermostat would act byconverting its lighter liquid into vapor would be 200. By making thevertical distance gf 17.17 inches the action would begin at thetemperature of 172 Fahrenheit. In the case of another liquid (not water)the action would be similar, and would 6o follow the law of the relationbetween the temperature and the tension of the saturated vapor of theliquid used.

Having described our invention, what we claim, and desire to secure byLetters Patent, is-

1. In an electrical thermostat, the combination of mercury with a4volatile liquid of different specific gravity, both contained in asuitable holder and relatively arranged sub- 7o stantially as described,whereby when said volatile liquid becomes a vapor by the application ofheat the mercury is suiciently displaced to close or break an electriccircuit, as set forth. 7 5

` 2. An opencircuit electrical thermostat, composed of a glass tubeclosed at one end and open at the other, and containing mercury and alighter volatile liquid, a holder for said tube, and two electrodesarranged to be electrically connected by mercury displaced from saidtube, asset forth.

3. A combination of areservoir containing a `liquid which at agiven'pressure volatilizes at a given temperature, to be indicated bymaking or breaking an electric circuit, and alsov a mobile electricalconductor, ksaid reservoir being sealed on the side intended to containthe Volatile liquid, with two electrodes adapted to be electricallyconnected or disconnected by the movement of the mobile electricalconductor within 'the reservoir under the increasing tension of thevaporized volatile liquid, substantially as described.y

FREDERICK H.A PREN TISS. JAMES A. TILDEN.

